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An MPGD Application: Muon Tomography for Detection of Nuclear Contraband

An MPGD Application: Muon Tomography for Detection of Nuclear Contraband. Marcus Hohlmann, P. Ford, K. Gnanvo, J. Helsby, R. Hoch, D. Mitra Florida Institute of Technology. 2 nd meeting of RD51 collaboration, Institute Henri Poincar é , Oct 13, 2008. Outline. Nuclear Contraband

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An MPGD Application: Muon Tomography for Detection of Nuclear Contraband

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  1. An MPGD Application:Muon Tomography for Detection of Nuclear Contraband Marcus Hohlmann, P. Ford, K. Gnanvo, J. Helsby, R. Hoch, D. Mitra Florida Institute of Technology 2nd meeting of RD51 collaboration, Institute Henri Poincaré, Oct 13, 2008

  2. Outline • Nuclear Contraband • Muon Tomography • Basic Concept • Existing Work • MPGDs for MT • Simulation of an MT station • Computing, Generation, Simulation, Reconstruction • Results on Expected Performance • Plans for R&D on MT Prototypes with MPGDs M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  3. The Nightmare Scenarios • Terrorist smugglehighly enriched uranium (HEU) or plutonium across borders and destroy a city by detonating a nuclear bomb, or • Terrorists smugglehighly radioactive material into a city and disperse it with a conventional explosion (“dirty bomb”) making portions of the city uninhabitable. T.B. Cochran and M.G. McKinzie, Scientific American, April 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  4. Challenge in Detecting Nuclear Contraband • In 2002, reporters managed to smuggle a cylinder of depleted uranium shielded in lead in a suitcase from Vienna to Istanbul via train and in a cargo container through radiation monitors into NY harbor. Cargo was flagged for extra screening, but DU was not sensed. • In 2003, used route Jakarta – LA, same result ~ 800 Radiation Portal Monitors (n,γ) in U.S. Sci. Am.,4/2008 6.8 kg DU • IAEA: During 1993-2006, 275 confirmed incidents with • nuclear material and criminal intent; 14 with HEU, 4 with Pu. Sci. Am., 4/2008 HEU can be hidden from conventional radiation monitoring because emanating radiation is relatively easy to shield within regular cargo Scientific American, April 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  5. A Potential Solution: Muon Tomography Note: angles are exaggerated ! Incoming muons (μ±) (from natural cosmic rays) Q=+92e μ μ Cargo container Q=+26e Θ 235U 92 Θ hidden & shielded high-Z nuclear material 56Fe 26 HEU: Big scattering angles! μ Θ Regular material: small scattering angles Θ Approx. Gaussian distribution of scattering angles θ withwidth θ0: Tracking Detector • Main ideas: • Multiple Coulomb scattering is ~ prop. to Z and could discriminate materials by Z • Cosmic ray muons are ubiquitous; no artificial radiation source or beam needed • Muons are highly penetrating; potential for sensing high-Z material shielded by Fe or Pb • Cosmic Ray Muons come in from many directions allowing for tomographic 3D imaging μtracks M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  6. MT Work by Other Groups Original idea from Los Alamos (2003): Muon Tomography with Drift Tubes INFN Padova, Pavia & Genova: Muon Tomography with spare CMS Muon Barrel Chambers (Drift Tubes) CMS Muon barrel J.A. Green et al., “Optimizing the Tracking Efficiency for Cosmic Ray MuonTomography”, LA-UR-06-8497, IEEE NSS 2006 S. Pesente et al., SORMA West 2008, Berkely, June 2008 Pb W Cu Brass Fe Al Efforts also by Tsinghua U., IHEP Protvino, Decision Science (U.S. commercial) M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  7. Fl. Tech Concept – MT with MPGDs Use Micro Pattern Gaseous Detectors for tracking cosmic ray muons • ADVANTAGES: • excellent spatial resolution • improves scattering angle • measurement • compact detector structure allows • for more compact MT station design • thin detector layers • small gaps between layers • smaller scattering in detector itself • CHALLENGES: • requires large-area MPGDs (MPGDs as muon detector !) • large number of electronics channels (but occupancies very low) • low rates from cosmics, need good eff. • cost (but access to funding outside HEP) • That’s why we’re here today! Cargo container MPGD Tracking Detector hidden & shielded high-Z nuclear material μ Θ Θ MPGD, e.g. GEM Detector MPGD Tracking Detector ~ 1 cm e- μtracks Readout electronics F. Sauli M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  8. Where’s Florida Tech ? Cape Canaveral & NASA Kennedy Space Center Orlando (IEEE NSS ‘09) Physics & Space Sciences Dept. Florida Tech • Small, private university on the “Space Coast” • founded by a physicist in 1958 • ~2,500 undergrads & ~2,500 graduate students • Muon Tomography Group: • 2 faculty (HEP, Comp. Sci.) • 1 post-doc • 2 graduate students • 4 undergraduates • (1 electronics engineer) Photo credit: NASA STS-95 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  9. We are currently here R&D Program Three-year program: • Build a Linux cluster for simulation work (160 slots; on Grid via OSG; could be made available to RD51!) • Detailed MC simulation of MT station • Prototyping with increasing detector size • Performance measurements Funded by Domestic Nuclear Detection Office (DNDO) in the U.S. Department of Homeland Security (DHS) (Disclaimer: The views and conclusions contained in this presentation are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Department of Homeland Security.) M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  10. Top View 5m CRY plane 3m GEMs Monte Carlo Simulation Typical Geometry: • Generate cosmic ray muons with CRY(Lawrence Livermore NL) • Simulate geometry, target, detector, tracks with GEANT4 • Take advantage of detailed description of multiple scattering effects within GEANT4 (follows Lewis theory of multiple scattering) Side View 10m Muons originate here over an area of 1,000,000 cm2 (1M muons in ~1min exposure) 4m Basic Target GEM detector planes 3 GEM layers with 5mm gaps between layers 10m - + 4m M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  11. Geometrical Acceptance Side View (x-z plane) Top View (x-y plane) MT station type Top & bottom detectors only z 3m y x Top, bottom & side detectors z y x Traversal of station by cargo M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  12. Simple reconstruction algorithm using Point of Closest Approach (“POCA”) of incoming and exiting 3-D tracks Treat as single scatter Scattering angle: Scattering Reconstruction M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  13. Scattering Angle Distributions Results from high-statistics MC samples M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  14. Basic Statistic for Z-discrimination: Mean Scattering Angles MT Station & Scenario: • Top, bottom & side det. • 40cm  40cm  10cm targets; 5 materials • Divide volume into voxels Results: • Good Z discrimination (even for Pb vs. U) • Targets imaged • Resolution matters! W U W U Pb Pb Al Fe Al Fe W W U U Pb Pb Al Fe Al Fe M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  15. Effect of Detector Material Comparison: 1. All MT station materials set to vacuum 2. Station volume filled with air;GEMs modeled by 5mm Kapton material Result: Minor increase in mean scattering angles and image smearing M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  16. U U U W W W Pb Pb Pb Significance of Excess – 10min • 10 minexposure • Compare targets against Fe back- ground (steel) using Fe samples w/ high statistics • Significance for all voxels with an excess at ≥ 99% confidence level over Fe standard: Sig Sig W U Pb > 5σ in ALL high-Z voxels Sig Sig M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  17. U U U W W W Pb Pb Pb Significance of Excess – 1min • 1 minexposure • Significance for all voxels with an excess at ≥ 99% confidence level over Fe standard • Still doing ok with 50 micron resolution • With 200 micron resolution we are losing sensitivity Sig Sig U W Pb Most U voxels > 3σ Sig Sig Trouble… M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  18. W W W U U U Pb Pb Pb Identifying Uranium at 99% C.L. • Test hypothesis that voxels with an excess over Fe actually contain U • Flag only voxels where mean voxel is within 99% confidence interval around expected mean U for Uranium (based on high-statistics U samples) 1 minexposure 10 minexposure W U Pb some false pos. correct pos. ID false positives false pos. correct pos. ID Pb target rejected by U hypothesis ! false pos. false pos. false negative ! M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  19. 15cm 10cm Shielded Targets among Stack of Shielding Plates Reconstructed scattering angles (normalized) 10 min exposure Perfect resolution Side Views U Al plates Pb Decent Signal Targets: 10cm  10cm  10cm U cube encased by 2.5cm Pb on each side U Pb Fe plates 15 cm thick shielding plates made of Al or Fe No Signal “Vertical Clutter” Scenario M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  20. Advanced Reconstruction Algorithm Maximum Likelihood Method • Reproducing Los Alamos Expectation Max. algorithm (L. Schultz et al.) • Input: Use lateral shift Δxi in multiple scattering as additional information on top of scattering angle θi for each (i-th) muon track • Output:Scattering density λkfor each (k-th) voxel of the probed volume • λ relates the variance of scattering with radiation length (or Z value) of the respective material • Procedure: Maximize log-likelihood for assignment of scattering densities to all independent voxels given observed  tracks • Analytical derivation leads to an iterative formula for incrementally updating λk values in each iteration  First reconstruction of 40cm  40cm  20cm U target θi Δxi  Work in Progress… M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

  21. Conclusion & Plans • Muon Tomography with MPGDsis a promising technology for detecting shielded nuclear contraband as indicated by our MC studies • Good Z-discrimination expected for • U vs. Fe with 1 min exposure • U vs. Pb with 10 min exposure • Resolution and statistics dominate expected performance • MPGDs • offer significant performance improvement over drift tube stations due to superior resolution • allow much more compact MT stations • Plans: • Finalize simulation results; continue developing algorithms (CS people) • Move from simulation to experimentation • Build increasingly large MPGD prototypes and test them for MT • Partner with RD51 collaborators in this development of MPGDs for large-area muon chambers including electronics development We expect this experimental program to be a major challenge ! M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

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